A significant portion of the crude oil purchased by refineries is obtained from relatively small, low volume wells. Wells of this type have an output of less than 100 gallons per hour, and typically have an output in the range of 15 to 25 gallons per hour.
The oil from the well is usually supplied to a device which is commonly called a "heater treater". The heater treater is a baffled vessel which has a quantity of hot water at the bottom and pressurized gas thereabove, and the crude oil is introduced into the water at the bottom of the heater treater. A layer of floating oil will slowly build up on the surface of the water and, when a predetermined quantity of oil has built up, the increased fluid pressure will activate a valve which discharges some of the oil from the heater treater, typically about 6 to 8 gallons. A discharge of this type will usually occur every 5 to 25 minutes, depending on the volume of the associated well.
The oil discharged from the heater treater contains a residual quantity of water which is normally about three percent but, depending on the particular well, can be as high as eight percent or nine percent. This amount of water presents a serious problem, because a refinery will typically not purchase oil having a water content greater than a specified percentage, which is usually about one-half of one percent. It is thus important to remove as much water as possible from the oil in order to ensure that the oil will be readily marketable.
The specific gravity of crude oil is typically less than 1.0, and a traditional approach to separating two fluids having different specific gravities is to place a receptacle containing a mixture of the fluids into a centrifuge, thereafter turn on the centrifuge and rotate the receptacle at a high rate of speed in order to effect a separation of the fluids through centrifugal force, then stop the centrifuge and remove the receptacle, and then remove one of the separated liquids from the receptacle utilizing a further apparatus. A centrifuge of this type is, however, impractical for use in association with a small oil well, because it does not operate continuously, but rather in discrete separating cycles, and because either manual operation or an expensive control apparatus is required in order to effect the cyclic loading, actuation, deactuation and unloading of the centrifuge.
It is therefore an object of the invention to provide an improved centrifuge which can efficiently separate water from crude oil, and which is capable of continuous and unattended operation for long periods of time.
A further object of the invention is to provide a centrifuge, as aforesaid, which is structurally simple, relatively compact, and relatively inexpensive to manufacture and operate, so that it will be economically feasible to utilize it in conjunction with an oil well of relatively low volume.
A further object of the invention is to provide a centrifuge, as aforesaid, which is rugged and dependable and requires minimal maintenance.